Fuel Evaporation Control on Models With Catalytic Converter

OPERATION
The fuel evaporation control line of the fuel tank is connected to the activated carbon filter, in which the fuel vapors which accumulate in the tank are collected. The activated carbon filter is linked by means of two further lines to the air manifold. A fuel evaporation control valve is installed in these lines. When the fuel evaporation control valve is open, the vacuum in the air manifold draws in fresh air to the activated carbon filter. The fresh air flushes out the fuel collected in the filter and routes it to the engine, i.e. to the combustion process.

Since this additionally supplied mixture influences combustion to a considerable extend, the fuel evaporation control valve consists of a non-return valve and an electrically operated valve. Due to the non-return valve, the fuel evaporation control valve is closed initially when no power is applied. The non-return valve prevents fuel collecting in the air manifold when the vehicle is parked. This non-return valve opens as vacuum increases in the air manifold. Electrical activation takes place dependent on engine speed and load. The venting cycle (flushing phase) begins as soon as the emission (lambda) control system is active. On completion of one cycle, the valve is closed for approx. 1 min. (rest phase).